1. Field of the Invention
The present invention relates to Media Access Control (MAC) based on a Ubiquitous Sensor Network (USN), and more particularly, to an apparatus and method for controlling multi-channel access in USN-based MAC.
The present invention is derived from a research project supported by the Information Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) and the Institute for Information Technology Advancement (IITA) [2005-S-106-03, Development of Sensor Tag and Sensor Node Techniques for RFID/USN].
2. Description of the Related Art
USN-based MAC technologies aim at increasing the reliability of a network and increasing the lifetime of the network by reducing energy consumption. To this end, it is important to develop multi-channel MAC technologies capable of supporting multi-channel access of sensor nodes.
The use of multi-channel access can provide a reliability increase and a power consumption reduction resulting from a decrease in collision-caused loss, thus making it possible to increase the lifetime of a USN network and satisfy Quality of Service (QoS) requirements. Therefore, a multiple access scheme can be said to be very important.
Because multi-channel wireless sensor networks have small hardware sensors operated by small batteries, they have important differences from general multi-channel wireless networks.
A general sensor node radio-frequency (RF) module uses a single half-duplex radio transceiver. Thus, the sensor node RF module is inferior in hardware capability to applications used in general wireless ad-hoc environments. In general, one sensor node RF module is used because the sensor node is small.
Also, in general, a sensor node in a wireless sensor network uses a battery, which is difficult to replace by a new one, as a power source. Therefore, the sensor node cannot continue to maintain a receiving mode due to a limited power and thus uses a power-saving design that alternates between a sleep mode and a listening mode.
The main object of using a multi-channel wireless sensor network in the sensor network having such hardware limitations is to provide a power gain by minimizing retransmission that may be caused by a short latency and, in many cases, a collision.
Sensor networks can be used to monitor surrounding environments or natural environments that may have urgent situations such as forest fires, emergent patients, and traffic accidents. There is a case where a plurality of sensor nodes simultaneously transmit data to a sink node in the monitoring process. In this case, when only a single channel is used, the use of a contention-based MAC protocol may cause a failure in data transmission due to a severe contention or an increase in power loss due to retransmission. On the other hand, the use of a noncontention-based MAC protocol can provide a considerable latency but requires a constant amount of energy consumption for the considerable latency even in the normal mode.
Thus, unlike a multi-channel wireless access control scheme for a general wireless network, a multi-channel wireless access control scheme for a wireless sensor network must give special consideration to the limited battery lifetime and the QoS for urgent situations.